I. Field of the Invention
The present invention relates to a method for solderless connection of an electric actuator to a printed circuit, mainly for applications on motor vehicle dashboards.
II. Description of Related Art
The traditional methods of soldering electronic components onto printed circuits, whether through-hole mounted or surface mounted devices (SMD), are already known in the prior art. For example, the so-called wave method allows soldering of through-hole mounted components placed on the printed circuit by means of a wave of tin and lead which comes into contact with the printed circuit, and thus to solder the components. Another example is the so-called reflow method, which consists of passing the printed circuit, on which the components are pre-positioned with a mix of tin and lead (soldering paste), through a series of furnaces with different temperature levels. This method is currently the most widespread for soldering SMD components and has a number of advantages over the wave method, since it allows more efficient soldering and is less traumatic for all the components (it avoids bridges and shadow zones).
However, changes in environmental standards are rendering these techniques obsolete and dangerous for the environment, since they still require the use of lead, which reduces the melting temperature in tin-based soldering pastes (typically to 180° C.). Lead-free solutions have therefore been developed in compliance with new directives such as, for example, the RoHS directive (Restriction of Hazardous Substances), which bans any substance that is harmful for the environment, in particular lead, from soldering pastes.
The new soldering pastes used, almost entirely made from tin, therefore have the disadvantage of requiring higher melting temperatures (around 220-230° C.), which can damage the electric actuators and/or certain fragile components mounted on the printed circuit.
It is therefore necessary to develop new connector technology solutions.
Solutions exist already in the prior art that resolve these problems by the insertion of female connectors, called tulip connectors, which are soldered on their own on the printed circuit before the actuator is positioned and which are designed to connect and support the actuator. The actuator then has male connection pins, which allow the actuator to be electrically connected by insertion in the tulip connectors without any trauma for the actuator. These solutions have the disadvantage of being expensive and of often comprising a thermoplastic element designed to support the tulip connectors. In addition, while the electrical connection is guaranteed, the mechanical support is far from perfect, which can be detrimental to applications such as the micromotors used on motor vehicle dashboards. In fact, the printed circuit+actuator assembly is subjected to potentially considerable vibrations and there is a real need for good mechanical support. For this reason, it is traditionally necessary to add a part that will mechanically support the actuator on the circuit, for example a flange. This increases the production cost and adds an extra step to the assembly of the actuator.
Another connection mode called press-fitting also exists, which does not require soldering and allows electrical connection by mechanical deformation of a connector in a drill hole of the printed circuit.
The actuator can therefore be connected without soldering to the connector. This solution is practical since it does away with the need to solder the components, but is also has certain disadvantage: the force of insertion on the printed circuit is considerable, which can damage said circuit, and the connectors and the drill holes on the printed circuit must have accurate manufacturing tolerances in order to ensure sufficient mechanical support.
The state of the art includes, in particular, international patent application WO2005/032224 in which the metal plug to be fixed has a diameter greater than that of the receiving hole made in the printed circuit. For this reason, the insertion is carried out by mechanical retention in the printed circuit. The connection stress is high, creating constraints that are detrimental to the printed circuit. This solution also provides for soldering after positioning the element to be connected.
U.S. Pat. No. 3,670,409 presents another solution in which conductive sheets are fixed to a printed circuit by means of an adhesive.